[rtl,pwrmgr] Remove CONTROL lock due to low_power_hint
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@matutem is already working on this.
Since Jun 11, 2024.
Component:RTL
IP:pwrmgr
Priority:P2
Type:FutureRelease
- Dominant language
- SystemVerilog
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Description
### Description
The pwrmgr RTL locks the CONTROL CSR when low_power_hint is set. This feature is not documented and there is no record of the reason why it is implemented. This can also cause trouble, and https://github.com/lowRISC/opentitan/pull/23500 fixes one problem derived from it. This fix causes CONTROL to be locked when low_power_hint is on AND core is sleeping, so there is no way the CPU could actually write to CONTROL, and it reduces the scope of this locking to the point it may be almost useless.
In light of all this, I propose we remove the feature altogether in some future release.
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